1. Field of the Invention
The present invention relates to an imaging device and imaging method that alleviate light source flicker, even in situations where a subject is illuminated by exterior lighting for which an amount of flicker varies periodically.
2. Description of the Related Art
At the time of shooting a movie indoors or performing Live view display, a light source such as a fluorescent lamp may vary in brightness periodically in synchronization with frequency of the mains power supply, and have an adverse effect on Live view display or movie shooting. This phenomenon is called light source flicker, and in a situation where frame rate at the time of shooting or at the time of Live view display is not synchronized to the frequency of variation in light source brightness there will be variation in brightness for every frame (called surface flicker), and bright lines are caused in images within the same frame for each space period (called line flicker).
In order to reduce the effect of the above-described light source flicker, various technologies have previously been proposed. Such technology is disclosed, for example, in Japanese patent laid-open No. Hei. 11-122513 (hereafter referred to as patent literature 1) and Japanese patent laid-open No. Hei. 6-105204 (hereafter referred to as patent literature 2). With these prior art technologies, at the time of correction for the effect of light source flicker, first image data is acquired for frames using an image sensor of a camera, frequency of light source flicker is detected based on time transformation of brightness output of the acquired image data, and brightness gain of each frame acquired from the image sensor is corrected based on this detected flicker frequency so that brightness of images in each frame becomes uniform.
Flicker of a light source used for an indoor light source fluctuates at 50 Hz or 60 Hz since it is based on the commercial power supply frequency. For example, with patent publication 1, flicker detection is carried out by operating at a frame frequency that is the same as or slower than the flicker frequency of the light source, and confirming vertical intensity distribution of a frame. This method can not carry out flicker detection and correction effectively in a situation where live view display or movie recording is carried out at a frame frequency that is the same as or slower than the flicker period of the light source.